VOC Sources Research Articles

Study and Application of Test Method for VOCs Emission Factor of Refueling in Service Station

VOCs emission of service station is one of the main sources of VOCs in Beijing. Uncontrolled emission factor (UEF) of refueling in China, US EPA, EEA respectively is 2.16, 1.31 and 1.00 times of CARB UEF (1008 mg·L-1). China's gasoline standards have changed in the last 20 years, and there is an urgent need to carry out the localization of gasoline refueling VOCs emission factor research. This paper compared test methods for refueling emission factors of European Union (EU) and California Air Resources Board (CARB) and found that the EU method was simpler and easier to operate than the CARB method, so we processed refueling VOCs emission factors test device in reference to EU test methods and chose a set of United States Stage Ⅱ vapor recovery system in Beijing service stations to carry out studies on VOCs emission factors. The results showed that: 1 For the fuel test tank, refueling vapor recovery efficiencies were 0.93 and 0.83 times of air to liquid volume ratio (A/L) of Stage Ⅱ respectively in winter and summer. Refueling emission factor in summer was greater than that in winter, and its recovery efficiency was lower than that in winter. 2 For the social vehicles, winter and summer refueling UEF respectively was (525±42) mg·L-1 and (963±174) mg·L-1, at the same time was 0.52 and 0.95 times of CARB refueling UEF (1008 mg·L-1) in A/L=0.The average value of emission factors respectively was (55±30) mg·L-1 and (112±108) mg·L-1 in A/L 1.05-1.07 in winter and summer. 3Refueling UEF without vapor recovery of social vehicles was chosen as the localized summer and winter refueling UEF in Beijing, we could calculate the emission factor of vapor recovery in different A/L combining with the linear equation of the fuel test tank.

Effects of Climate Change on Environmental Hazards in Local Communities: A Data Visualization Prototype

Introduction: Although the effects of climate change on health risk have been extensively studied, it is unclear how climate change affects exposure pathways for environmental hazards. We create data visualization maps that inform policy makers to identify areas and people at greatest risk. Methods: Working with the EPA Toxics Release Inventory (TRI) Program and the Society for Chemical Hazard Communication (SCHC), we leveraged publicly available data (e.g. from the TRI, State health and environmental agencies, and NOAA and Landsat satellites) to develop an interactive web portal to display and communicate potential health and environmental effects of climate change on a disadvantaged neighborhood: the Near West Neighborhood. We created visualizations to identify: 1) locations at increased risk of flooding and associated vulnerabilities with respect to housing structures (mold), other critical infrastructure (including hospitals and schools), and contaminated sites and repositories for waste; 2) areas with an increased level of ozone formation from mobile and non-mobile sources of VOCs as they relate to increases in overall ambient temperature and localized urban heat island effects; and 3) hotspots where residents are more vulnerable to acute cardiovascular emergency call and hospitalization as a result of urban heat island effects. Results: these maps may aid decision-makers in identifying targeted areas and/or at-risk populations for disaster prevention, preparation, and response as a result of climate change and provides a cost-effective way to mitigate potential impacts of climate change. We have gained permission from the Near West Neighborhood to display this tool in the Neighborhood’s community center so the residents are empowered for environmental justice. Conclusion: the mapping tool will be invaluable for policy makers, as evidenced by our first prize award for the NIH/NIEHS Climate Change and Environmental Exposure Challenges. http://arcg.is/1K1mElG

Method to establish the emission inventory of anthropogenic volatile organic compounds in China and its application in the period 2008–2012

Abstract A method was developed to establish a comprehensive anthropogenic VOC emission inventory in China, in which a four-level source categorization was proposed, and an emission factor determination system together with a reference database were developed. And this was applied to establish VOC emission inventories for the period 2008–2012. Results show China's anthropogenic VOC emissions increased from 22.45 Tg in 2008 to 29.85 Tg in 2012 at an annual average rate of 7.38%, with Shandong, Guangdong, Jiangsu, Zhejiang and Hebei provinces being the largest emitters. Industrial processes, transportation and solvent utilization were the key sources, accounting for 39.3%, 25.6%, and 14.9% of the total emissions in 2012, respectively. Passenger cars, biofuel combustion, coke production, field burning of biomass, and raw chemical manufacturing were the primary VOC sources nationwide. The key sources for each province were different because of the disparate industry and energy structure. China's VOC emissions displayed remarkable spatial variation, with emissions in the east and southeast regions being much larger than in the northwest, and the high emission areas mainly centered in the Bohai Economic Rim, the Yangtze River Delta, the Pearl River Delta and the Sichuan Basin. The size of high emission areas expanded over the period 2008–2012, with heavily polluted city clusters gradually emerging.

Non-methane hydrocarbons (NMHCs) and their contribution to ozone formation potential in a petrochemical industrialized city, Northwest China

Hourly air concentrations of fifty-three non-methane hydrocarbons (NMHCs) were measured at downtown and suburb of Lanzhou, a petrochemical industrialized city, Northwest China in 2013. The measured data were used to investigate the seasonal characteristics of NMHCs air pollution and their contributions to the ozone formation in Lanzhou. Annually averaged NMHCs concentration was 38.29 ppbv in downtown Lanzhou. Among 53 NMHCs, alkanes, alkenes, and aromatics accounted for 57%, 23% and 20% of the total NMHCs air concentration, respectively. The atmospheric levels of toluene and propane with mean values of 4.62 and 4.56 ppbv were higher than other NMHCs, respectively. The ambient levels of NMHCs in downtown Lanzhou were compared with measured NMHCs data collected at a suburban site of Lanzhou, located near a large-scale petrochemical industry. Results show that the levels of alkanes, alkenes, and aromatics in downtown Lanzhou were lower by factors of 3-11 than that in west suburb of the city. O3-isopleth plots show that ozone was formed in VOCs control area in downtown Lanzhou and NOx control area at the west suburban site during the summertime. Propylene-equivalent (Prop-Equiv) concentration and the maximum incremental reactivity (MIR) in downtown Lanzhou indicate that cis-2-butene, propylene, and m/p-xylene were the first three compounds contributing to ozone formation potentials whereas in the petrochemical industrialized west suburb, ethane, propene, and trans-2-Butene played more important role in the summertime ozone formation. Principal component analysis (PCA) and multiple linear regression (MLR) were further applied to identify the dominant emission sources and examine their fractions in total NMHCs. Results suggest that vehicle emission, solvent usage, and industrial activities were major sources of NMHCs in the city, accounting for 58.34%, 22.19%, and 19.47% of the total monitored NMHCs in downtown Lanzhou, respectively. In the west suburb of the city, however, vehicle emission was less important as compared with sources from petrochemical industries, as characterized by relatively higher ethane (C2H4)/ ethyne (acetylene) and propene (C3H6)/ethyne ratios which ruled out tailpipes emission as major contributors to the VOCs sources.

수성페인트-실란접착제 혼합물의 접착특성

페인트는 외부로부터 본체가 손상되는 것을 막아주며, 오랫동안 색깔과 마무리 상태를 유지해 준다. 유기용제와 물이 페인트의 용제로 사용되고 있으며, 유기용제는 VOCs의 인위적인 공급원으로 알려져 있다. 이러한 이유로 자동차 내장부품에서 유기용재 페인트의 사용은 줄어들고 있으며, 외장 부품에서는 계속 사용하고 있다. 수성페인트의 접착력은 유성페인트에 비하여 작아, 페인트가 기제로부터 박리되고 있어, 품질문제를 일으킨다. 본 연구에서는 수성페인트와 실린 혼합물의 접착 특성에 대하여 연구하였다. 수성페인트의 접착력을 향상시키기 위하여 접착제와 혼합이 필요하다. 접착력은 UTM을 이용하여 ASTM D1002 방법으로 측정하였고, 박리현상은 ASTM D1002를 사용하여 측정하였다. 수성페인트와 실란접착제의 최적 혼합조건은 <TEX>$25^{\circ}C$</TEX>, 500rpm, 20분 이었으며. 실란접착제 농도는 5wt% 이었다 Paint must be resistant to the wear and tear of the atmosphere and should maintain its color and finish for a long time. The solvents of paints were organic solvent and water, common artificial source of VOCs(Volatile organic Solvent) include organic solvent. Using of organic solvent paint was decreased in the interior parts of automotive, exterior parts were still used organic solvent paint. Adhesive strength of water-paint was poor to compare with organic solvent paint and peeled off from the base materials, it was big quality problem. In this study, adhesive characteristics of water-paint and silane mixture was investigated. To improve adhesive strength of water-paint, it was necessary to mixing of adhesive material. Adhesive strength was measured using UTM(Universal Test Instrument) by ASTM D1002 and Peeling off condition was by ASTM D3359. Optimal mixing condition of water-paint and silane adhesive were <TEX>$25^{\circ}C$</TEX>, 500rpm, 20min., concentration of silane adhesive was 5 wt%.

Metabolic changes in Citrus leaf volatiles in response to environmental stress

Citrus plants are well known as a rich source of VOCs, and several have important roles in defense responses. However, how VOCs are regulated in response to environmental stress is not yet well understood. In this study, we investigated dynamic changes of VOCs present in leaves of seven Citrus species (Citrus sinensis, C. limon, C. paradisi, C. unshiu, C. kinokuni, C. grandis, and C. hassaku) in response to mechanical wounding, jasmonic acid (JA), and salicylic acid (SA) as determined by gas chromatography/mass spectrometric analysis followed by multivariate analysis (principal component analysis, PCA, and orthogonal partial least squares-discriminant analysis, OPLS-DA). PCA and OPLS-DA suggested that changes in VOC profiles against stress stimuli were much diverse among Citrus species. OPLS-DA showed that C6 volatiles, such as hexanal and trans-2-hexenal, were induced in response to JA and SA stimuli in C.sinensis and C.grandis, while the other VOCs were decreased under all tested stress conditions. α-Farnesene was induced in all species except C.hassaku after wounding or JA treatment. In addition, α-farnesene was also induced in response to SA stimuli in C.unshiu and C.kinokuni. Therefore these volatiles can be candidates of the common stress biomarkers in Citrus. Our results will give a new insight into defense mechanisms in Citrus species.

The vapor-phase multi-stage CMD test for characterizing contaminant mass discharge associated with VOC sources in the vadose zone: Application to three sites in different lifecycle stages of SVE operations

Vapor-phase multi-stage contaminant mass discharge (CMD) tests were conducted at three field sites to measure mass discharge associated with contaminant sources located in the vadose zone. The three sites represent the three primary stages of the soil vapor extraction (SVE) operations lifecycle—pre/initial-SVE, mid-lifecycle, and near-closure. A CMD of 32g/d was obtained for a site at which soil vapor SVE has been in operation for approximately 6years, and for which mass removal is currently in the asymptotic stage. The contaminant removal behavior exhibited for the vapor extractions conducted at this site suggests that there is unlikely to be a significant mass of non-vapor-phase contaminant (e.g., DNAPL, sorbed phase) remaining in the advective domains, and that most remaining mass is likely located in poorly accessible domains. Given the conditions for this site, this remaining mass is hypothesized to be associated with the low-permeability (and higher water saturation) region in the vicinity of the saturated zone and capillary fringe. A CMD of 25g/d was obtained for a site wherein SVE has been in operation for several years but concentrations and mass-removal rates are still relatively high. A CMD of 270g/d was obtained for a site for which there were no prior SVE operations. The behavior exhibited for the vapor extractions conducted at this site suggest that non-vapor-phase contaminant mass (e.g., DNAPL) may be present in the advective domains. Hence, the asymptotic conditions observed for this site most likely derive from a combination of rate-limited mass transfer from DNAPL (and sorbed) phases present in the advective domain as well as mass residing in lower-permeability (“non-advective”) regions. The CMD values obtained from the tests were used in conjunction with a recently developed vapor-discharge tool to evaluate the impact of the measured CMDs on groundwater quality.

Temporal and spatial variability of trace volatile organic compounds in rainwater

This study presents the first detailed concentration profile of trace VOCs in atmospheric waters. Analytes were detected and quantified in 111 unique rain events in Wilmington, NC, USA over a one-year period. Headspace solid phase microextraction was optimized for detection of these compounds at sub-nanomolar levels. Distinct seasonality in both the occurrence and concentration of compounds was observed with the lowest abundance occurring during low irradiance winter months. In contrast to other rainwater components studied at this location, VOCs did not show any correlation between rainfall amount and concentrations. There was significant spatial variation with regards to air-mass back-trajectory for methyfuran with higher concentrations observed in terrestrial events during the growing season. Air mass back trajectory also impacted CCl4 concentrations in rainwater with evidence of a possible oceanic input. However there was no significant impact of air-mass back-trajectory on the concentration of BTEX observed in rain indicating that storm origin is not the controlling factor driving concentrations of these analytes in precipitation. Members of the BTEX family did, however, have significant correlations with each other occurring in ratios aligned closely with ratios reported in the literature for gas-phase BTEX. Using available gas-phase data from locations with similar anthropogenic sources and Henry’s Law constants, calculated concentrations agreed with VOC levels found in Wilmington rain. Results of this study indicate local gas-phase scavenging is the major source of VOCs in rain and wet deposition is not an efficient removal mechanism (<0.1%) of VOCs from the atmosphere.

Levels and sources of volatile organic compounds including carbonyls in indoor air of homes of Puertollano, the most industrialized city in central Iberian Peninsula. Estimation of health risk.

Twenty nine organic air pollutants including carbonyl compounds, alkanes, aromatic hydrocarbons and terpenes were measured in the indoor environment of different houses together with the corresponding outdoor measurements in Puertollano, the most industrialized city in central Iberian Peninsula. VOCs were sampled during 8 weeks using Radiello(®) passive samplers, and a questionnaire on potential VOCs sources was filled out by the occupants. The results show that formaldehyde and hexanal was the most abundant VOCs measured in indoor air, with a median concentration of 55.5 and 46.4μgm(-3), respectively followed by butanal (29.1μgm(-3)), acetone (28.4μgm(-3)) and acetaldehyde (21.4μgm(-3)). After carbonyls, n-dodecane (13.1μgm(-3)) and terpenes (α-pinene, 13.4μgm(-3) and limonene, 13.4μgm(-3)) were the compounds with higher median concentrations. The indoor/outdoor (I/O) ratios demonstrated that sources in the indoor environment are prevailing for most of the investigated VOCs especially for limonene, α-pinene, hexanal, formaldehyde, pentanal, acetaldehyde, o-xylene, n-dodecane and acetone with I/O ratio >6. Multiple linear regressions were applied to investigate the indoor VOC determinants and Spearman correlation coefficients were used to establish common sources between VOCs. Finally, the lifetime cancer risk associated to formaldehyde, acetaldehyde and benzene exposure was estimated and they varied from 7.8×10(-5) to 4.1×10(-4) for formaldehyde, from 8.6×10(-6) to 3.5×10(-5) for acetaldehyde and from 2.0×10(-6) to 1.5×10(-5) for benzene. For formaldehyde, the attributed risk in most sampled homes was two orders of magnitude higher than the one (10(-6)) proposed as acceptable by risk management bodies.

Investigation of gasoline distributions within petrol stations: spatial and seasonal concentrations, sources, mitigation measures, and occupationally exposed symptoms.

We measured levels of VOCs and determined the distributions of benzene concentrations over the area of two petrol stations in all three seasons. Using the concentrations and sampling positions, we created isoconcentration contour maps. The average concentrations ranged 18-1288 μg m(-3) for benzene and 12-81 μg m(-3) for toluene. The contour maps indicate that high-level contours of benzene were found not only at the fuel dispenser areas but also at the storage tank refilling points, open drainage areas where gasoline-polluted wastewater was flowing, and the auto service center located within the station area. An assessment of the benzene to toluene ratio contour plots implicates that airborne benzene and toluene near the fuel dispenser area were attributed to gasoline evaporation although one of the studied stations may be influenced by other VOC sources besides gasoline evaporation. Additionally, during the routine refilling of the underground fuel storage tanks by a tank truck, the ambient levels of benzene and toluene increased tremendously. The implementation of source control by replacing old dispensers with new fuel dispensers that have an efficient cutoff feature and increased delivery speed can reduce spatial benzene concentrations by 77%. Furthermore, a questionnaire survey among 63 service attendants in ten stations revealed that headache was the most reported health complaint with a response rate of 32%, followed by fatigue with 20%. These prominent symptoms could be related to an exposure to high benzene concentrations.

Characterization of VOC sources in an urban area based on PTR-MS measurements and receptor modelling.

In this study, the concentrations of volatile organic compounds were measured by the use of proton transfer reaction mass spectrometry, together with NO x , NO, NO2, SO2, CO and PM10 and meteorological parameters in an urban area of Belgrade during winter 2014. The multivariate receptor model US EPA Unmix was applied to the obtained dataset resolving six source profiles, which can be attributed to traffic-related emissions, gasoline evaporation/oil refineries, petrochemical industry/biogenic emissions, aged plumes, solid-fuel burning and local laboratories. Besides the vehicle exhaust, accounting for 27.6% of the total mixing ratios, industrial emissions, which are present in three out of six resolved profiles, exert a significant impact on air quality in the urban area. The major contribution of regional and long-range transport was determined for source profiles associated with petrochemical industry/biogenic emissions (40%) and gasoline evaporation/oil refineries (29%) using trajectory sector analysis. The concentration-weighted trajectory model was applied with the aim of resolving the spatial distribution of potential distant sources, and the results indicated that emission sources from neighbouring countries, as well as from Slovakia, Greece, Poland and Scandinavian countries, significantly contribute to the observed concentrations.

Examining single-source secondary impacts estimated from brute-force, decoupled direct method, and advanced plume treatment approaches

In regulatory assessments, there is a need for reliable estimates of the impacts of precursor emissions from individual sources on secondary PM2.5 (particulate matter with aerodynamic diameter less than 2.5 microns) and ozone. Three potential methods for estimating these impacts using Eulerian grid photochemical models are the brute-force (B–F) method, the decoupled direct method (DDM), and advanced plume treatment (APT). Here, we systematically inter-compare and assess the B–F, DDM, and APT approaches using hypothetical sources in a consistent modeling platform for a wide range of source conditions (i.e., emissions amount and composition, location within two California air basins, and stack parameters). The impacts of NOx and VOC sources on ozone and SO2 sources on PM2.5 sulfate calculated by these methods are in general agreement. The agreement is evident in the similar magnitudes, spatial patterns, and strong correlations among the impacts. This result, along with previous model evaluations based on similar Eulerian grid modeling, builds confidence in the reliability of the impact estimates. Disagreement among methods is evident in calculations of PM2.5 nitrate impacts associated with NH3 and NOx sources. Numerical instabilities in DDM sensitivity calculations compromise the nitrate impact estimates from that approach. The B–F and APT methods, which use brute-force differencing to identify impacts, are affected by numerical artifacts to a lesser degree than (H)DDM, with the artifacts being more prominent for APT than B–F. Overall, our results indicate that the (H)DDM, B–F, and APT approaches are viable for use in estimating single-source impacts for ozone and secondary PM2.5 sulfate, while the B–F method appears to be the most reliable for estimating nitrate impacts. There is a need for additional field study measurements to better constrain model estimates of single-source secondary impacts.

Long-term trends in California mobile source emissions and ambient concentrations of black carbon and organic aerosol.

A fuel-based approach is used to assess long-term trends (1970-2010) in mobile source emissions of black carbon (BC) and organic aerosol (OA, including both primary emissions and secondary formation). The main focus of this analysis is the Los Angeles Basin, where a long record of measurements is available to infer trends in ambient concentrations of BC and organic carbon (OC), with OC used here as a proxy for OA. Mobile source emissions and ambient concentrations have decreased similarly, reflecting the importance of on- and off-road engines as sources of BC and OA in urban areas. In 1970, the on-road sector accounted for ∼90% of total mobile source emissions of BC and OA (primary + secondary). Over time, as on-road engine emissions have been controlled, the relative importance of off-road sources has grown. By 2010, off-road engines were estimated to account for 37 ± 20% and 45 ± 16% of total mobile source contributions to BC and OA, respectively, in the Los Angeles area. This study highlights both the success of efforts to control on-road emission sources, and the importance of considering off-road engine and other VOC source contributions when assessing long-term emission and ambient air quality trends.

Forecasting of VOC emissions from traffic and industry using classification and regression multivariate methods

In this study, advanced multivariate methods were applied for VOC source apportionment and subsequent short-term forecast of industrial- and vehicle exhaust-related contributions in Belgrade urban area (Serbia). The VOC concentrations were measured using PTR-MS, together with inorganic gaseous pollutants (NOx, NO, NO2, SO2, and CO), PM10, and meteorological parameters. US EPA Positive Matrix Factorization and Unmix receptor models were applied to the obtained dataset both resolving six source profiles. For the purpose of forecasting industrial- and vehicle exhaust-related source contributions, different multivariate methods were employed in two separate cases, relying on meteorological data, and on meteorological data and concentrations of inorganic gaseous pollutants, respectively. The results indicate that Boosted Decision Trees and Multi-Layer Perceptrons were the best performing methods. According to the results, forecasting accuracy was high (lowest relative error of only 6%), in particular when the forecast was based on both meteorological parameters and concentrations of inorganic gaseous pollutants.

A refined 2010-based VOC emission inventory and its improvement on modeling regional ozone in the Pearl River Delta Region, China

Accurate and gridded VOC emission inventories are important for improving regional air quality model performance. In this study, a four-level VOC emission source categorization system was proposed. A 2010-based gridded Pearl River Delta (PRD) regional VOC emission inventory was developed with more comprehensive source coverage, latest emission factors, and updated activity data. The total anthropogenic VOC emission was estimated to be about 117.4×104t, in which on-road mobile source shared the largest contribution, followed by industrial solvent use and industrial processes sources. Among the industrial solvent use source, furniture manufacturing and shoemaking were major VOC emission contributors. The spatial surrogates of VOC emission were updated for major VOC sources such as industrial sectors and gas stations. Subsector-based temporal characteristics were investigated and their temporal variations were characterized. The impacts of updated VOC emission estimates and spatial surrogates were evaluated by modeling O3 concentration in the PRD region in the July and October of 2010, respectively. The results indicated that both updated emission estimates and spatial allocations can effectively reduce model bias on O3 simulation. Further efforts should be made on the refinement of source classification, comprehensive collection of activity data, and spatial–temporal surrogates in order to reduce uncertainty in emission inventory and improve model performance.

Emissions from oil sands tailings ponds: Review of tailings pond parameters and emission estimates

The storage of large volumes of tailings has become an issue for Canada׳s oil sands industry. The use of diluent, along with incomplete bitumen and solvent recovery from the tailings stream, leads to the accumulation of organic compounds within tailings ponds. Volatile organic compounds, reduced sulfur compounds, carbon dioxide, and methane are emitted from tailings outfalls, oily films, bitumen slicks, and mature fine tailings. These emissions are linked to the bitumen extraction and tailings treatment processes, tailings properties (composition, age, residence time), and environmental factors (wind, temperature, rain, and ice cover). Due to limited research in this area, it is difficult to evaluate relationships between emission sources and compounds emitted. To estimate emissions, emission factors based on snapshot measurements, and varying models and assumptions are commonly used. This review presents current knowledge on factors and parameters influencing emission estimates, and challenges pertaining to the development of current emissions factors. Standard emission measurement and calculation methods, vigilant sampling, and increased research are needed to develop a more accurate and representative understanding of emissions from oil sands tailings ponds. • Oil sands tailings are heterogeneous sources of VOC, CO 2 , CH 4 , and RSC emissions. • Knowledge gap and research needs to improve emissions measurement were identified. • Understanding the impact of ice melt and microbial activity on emissions is needed. • Methods that capture the spatial and temporal variation of emissions are needed.

Measuring spatial variability of vapor flux to characterize vadose-zone VOC sources: Flow-cell experiments

A method termed vapor-phase tomography has recently been proposed to characterize the distribution of volatile organic contaminant mass in vadose-zone source areas, and to measure associated three-dimensional distributions of local contaminant mass discharge. The method is based on measuring the spatial variability of vapor flux, and thus inherent to its effectiveness is the premise that the magnitudes and temporal variability of vapor concentrations measured at different monitoring points within the interrogated area will be a function of the geospatial positions of the points relative to the source location. A series of flow-cell experiments was conducted to evaluate this premise. A well-defined source zone was created by injection and extraction of a non-reactive gas (SF6). Spatial and temporal concentration distributions obtained from the tests were compared to simulations produced with a mathematical model describing advective and diffusive transport. Tests were conducted to characterize both areal and vertical components of the application. Decreases in concentration over time were observed for monitoring points located on the opposite side of the source zone from the local-extraction point, whereas increases were observed for monitoring points located between the local-extraction point and the source zone. The results illustrate that comparison of temporal concentration profiles obtained at various monitoring points gives a general indication of the source location with respect to the extraction and monitoring points.

Source Apportionment of VOCs in Urban Tianjin, China

facing the problem of VOCs pollution, VOCs concentrations in urban Tianjin have been measured to identify their possible sources. Using positive matrix factorization, seven VOC sources are identified in urban Tianjin according to the factor loadings of various VOCs, including: 1) motor vehicle exhaust; 2) gasoline evaporation; 3) internal engine combustion emission; 4) diesel emission; 5) solvent usage; 6) industrial emission; and 7) biogenic emission. The identified sources of VOCs are significantly related to vehicular activities, which specifically contribute 60% to VOCs loadings in urban Tianjin, respectively. Controlling vehicle emissions should be top priority for VOCs reduction in Tianjin.

Aerosol oxalate and its implication to haze pollution in Shanghai, China

A total of 238 samples of PM2.5 and TSP were analyzed to study the characteristics, sources, and formation pathways of aerosol oxalate in Shanghai in four seasons of 2007. The concentrations of oxalate were 0.07–0.41 μg/m3 in PM2.5 and 0.10–0.48 μg/m3 in TSP, respectively. Oxalate displayed a seasonal variation of autumn > summer > winter > spring in both PM2.5 and TSP and was dominantly present in PM2.5 in all samples. Correlation between oxalate and K+ and high ratio of oxalate/K+ suggested that biomass burning was a secondary source of aerosol oxalate in Shanghai, in addition to urban VOCs sources (vehicular and industrial emissions), especially in autumn. Secondary formation accounted for the majority of aerosol oxalate in Shanghai, which was supported by the high correlation of oxalate with nss-SO4 2−, K+ and NO3 −, proceeding from different mechanisms. Relatively high ambient RH together with high cloud cover was found benefiting the secondary formation of aerosol oxalate. The in-cloud process (aqueous-phase oxidation) was proposed to be likely the major formation pathway of aerosol oxalate in Shanghai, which was supported by the high correlation of oxalate with nss-SO4 2− and K+, dominant residence of oxalate in droplet mode and result of favorable meteorological condition analysis. High correlation of oxalate and NO3 − reflected the OH radical involved oxidation chemistry of the two species in the atmosphere and also suggested that gas-particle surface reactions and the evaporation–condensation process were both possible secondary formation pathways of aerosol oxalate in coarser particle mode (>1.0 μm). As a major water-soluble organic compound in aerosols, concentration of oxalate showed a distinct negative correlation to the atmospheric visibility, which implied that aerosol organic compounds could play an important role in haze pollution as well as in air quality in Shanghai.

SOA Formation Potential of Emissions from Soil and Leaf Litter

Soil and leaf litter are significant global sources of small oxidized volatile organic compounds, VOCs (e.g., methanol and acetaldehyde). They may also be significant sources of larger VOCs that could act as precursors to secondary organic aerosol (SOA) formation. To investigate this, soil and leaf litter samples were collected from the University of Idaho Experimental Forest and transported to the laboratory. There, the VOC emissions were characterized and used to drive SOA formation via dark, ozone-initiated reactions. Monoterpenes dominated the emission profile with emission rates as high as 228 μg-C m(-2) h(-1). The composition of the SOA produced was similar to biogenic SOA formed from oxidation of ponderosa pine emissions and α-pinene. Measured soil and litter monoterpene emission rates were compared with modeled canopy emissions. Results suggest surface soil and litter monoterpene emissions could range from 12 to 136% of canopy emissions in spring and fall. Thus, emissions from leaf litter may potentially extend the biogenic emissions season, contributing to significant organic aerosol formation in the spring and fall when reduced solar radiation and temperatures reduce emissions from living vegetation.